Terpol ymers



TERPOLYMERS George L. Wesp, Englewood, and Robert J. Siocomhe,

Dayton, Ohio, assignors to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware Application December 7, 1953, Serial No. 396,481 l 24 Claims. (Cl. Zoli-80.5)

This invention relates to three-component interpolymers, commonly called terpolymers, i. e., interpolymers prepared by polymerizing a monomeric mixture consisting of three different monomers. In specific aspects the invention pertains to terpolymers of (a) acrylonitrile, (b) a monomer selected from the group consisting of a-acetoxystyrene, wmethylstyrene, styrene, vinyltoluene, vinylxylene, and (c) a different monomer selected from said group. Other aspects of the invention relate to improved methods of preparing clear terpolymers.

It is by now well known that ethylenically unsaturated monomers diier greatly in their polymerization reactivity toward each other. There are in fact some monomers that will not undergo homopolymerization at all, i. e., polymerization of two or more molecules of the same monomer to form a polymer of that monomer, yet will readily undergo interpolymerization with certain other monomers. Interpolymerization affords a method of imparting varying characteristics to a polymer, and in many instances such characteristics cannot be obtained by mere physical admixture of two or more homopolymers. However, because of the above-mentioned diierences in reactivity among monomers toward each other, marked heterogeneity is the rule in interpolymers and only under special circumstances can an interpolymer be obtained that is of sucient homogeneity to give a transparent or clear interpolymer. While some objectionable properties such as color, encountered in interpolymers, can often be avoided by means such as the use of stabilizers or lower polymerization temperatures, incompatibility manitested by haze, turbidit or opacity in plastics is not overcome by such treatment.

if a monomeric mixture is subjected to polymerization and the initial increment of polymer is segregated before the polymerization is allowed to go forward to an appreciable extent, it'is frequently possible to obtain a clear interpolymer, but the commercial impracticability of such a procedure is apparent. On the other hand, if polymerization is permitted to proceed to a considerable and especially to a high degree of conversion, the more reactive monomer enters into the polymer to a greater extent than a less reactive monomer or monomers with the consequence that residual unreacted monomer becomes more and more depleted in the more reactive monomer, while the polymer being formed in the latter stages of polymerization is deficient in the more reactive monomer. There results a polymeric material which is made up of a Variety of polymer molecules running a gamut of compositions such that the total polymer is heterogeneous with resultant opacity and often greatly impaired physical properties` This phenomenon, resulting in an undesirable product, can be overcome to an appreciable but limited extent by gradually adding during the course of the polymerization the more reactive monomer at a rate aimed at keeping the composition of unreacted monomeric mixture essentially constant. As a practical matter it is extremely dicult to approach uniformity in such an operation, and it is impossible to use this technique at nited States Parent all in the case of mass (bulk) polymerization in which the 1nolymerization reaction mixture sets up into semisolid or solid polymer after the reaction is only partly completed so that further access of added monomer to the total mixture cannot be obtained.

Itv is only in recent years that systematic laboratory and theoretical studies of interpolymerization have gone forward suiiicien'tly to permit a certain amount of predictability in this iield. It has been theorized that in a simple binary system involving the free-radical-initiated polymerization of only two monomers, the composition of polymer will be dependent only upon the rate of four propagation steps, i. e., steps in the propagation of poly mer molecules. Thus, taking a system invloving two monomers, M1 and M2, a growing polymer chain can have only two kinds of active terminal groups, i. e., a group derived from M1 or a group derived from M2. Either of these groups has the possibility of reacting with either M1 or with M2. Using m1- and m2' to indicate these active terminal groups, the four possible reactions are as follows:

Growing Adding Rate of Process Reaction Chain Monomer Product M'vmr' Mr k11['m1-][Mi] IMm11111- 'm1- Mz kizlmi- [M2] "W mima 'M mr M2 mima [Mil "12m2- "W TM- Mi kz1[ms-][ll/I|] Wumi- Theoretical considerations lead to the now generally accepted copolymer composition equation which describes the ratio of the molar` concentrations of two monomers in the initial copolymer formed from a given mixture of the monomers as follows:

ln this equation r1 equals 1cm/k12 and r2 equals k22/k21. The terms r1 and r2 are called reactivity ratios. A very considerable body of experimental work has in general confirmed the copolymer composition equation.

A large proportion of possible pairs of monomers are incapable, because of their respective reactivity ratios, of forming under any conditions an instantaneous polymer having the same composition as the monomeric mixture from which it is formed. However there are certain monomer pairs which, in a proportion characteristic of that pair, give a copolymer having the samecomposition as the particular monomeric mixture. In such instances, a batch polymerization can be carried out with a monomeric mixture of the particular composition with a resultant homogeneous copolymer containing the same relative proportions of the monomers as in the initial monomeric reaction mixture. This composition is known as the polymerization azeotrope composition, and is repre# sented by the equation:

Such an azeotrope composition can exist only for those monomer pairs wherein both r1 and r2 are less than one, or theoretically wherein both r1 and r2 are greater than one although no examples of the latter combination are known.

While an understanding of interpolymerization involving only two monomers is now possible to a considerable extent, because of the development of the above-disrs e) cussed theories, an increase in the number of monomers to three or more obviously tremendously increases the possibilities and complications. Thus, for example if interpolymers of 100 monomers are to be considered, there are about 5000 possible monomer pairs, but about 160,000 diierent combinations of three monomers are possible, and for each of these 160,000 combinations the variations in relative proportions of the three monomers are infinite. lf the assumptions made in the development of the copolymer composition equation still hold true where three monomers are to be interpolymerized, it is apparent that the composition of the terpolymers formed at any given instance will now be dependent upon the rate of nine propagation steps which are dependent upon the relative concentrations of the monomers in the monomeric mixture and the reactivity ratio between each of thc pairs of the monomers in the mixture. It has been pointed out that the study of terpolymers can be simplied somewhat by application of the copolymer composition equation, suitably modified for three-component systems, so as to eliminate from consideration monomers whose ability to interpolymerize is so slight that further investigation of such combinations is obviously not warranted. However, the discovery of terpolymers having particularly desired physical properties has to the present time been limited to the needle in the haystack type of investigation. There is an obvious need for some procedure in the terpolymer field whereby terpolymers of particular properties can be made with a reasonable degree of predictability.

In accordance with the present invention, we have found a group of terpolymers that can be made by freeradical-initiated batch polymerization and that have the very desirable property of clarity. These terpolymers are made by polymerizing a monomeric mixture of certain proportions of thee monomers. The proportions giving clear terpolymers will vary from one monomeric mixture to another depending upon the particular monomers present in that mixture. The invention is particularly applied to monomeric mixtures consisting essentially of (a) acrylonitrile, (b) a monomer selected from the group consisting of a-acetoxystyrene, a-methylstyrene, styrene, vinyltoluene, vinylxylene, and (c) a different monomer selected from the same group listed under (b). For example, a monomeric mixture consisting of acrylonitrile, a-methylstyrene, and styrene will, when subjected to freeradical-initiated batch polymerization, give a clear terpolymer only if the relative proportions of acrylonitrile, m-methylstyrene and styrene are properly chosen in a manner to be hereinafter described. In contrast, a monomeric mixture consisting of acrylonitrile, styrene, and vinyltoluene will give a clear terpolymer on being subjected to free-radical-initiated batch polymerization only if the relative proportions of the three mentioned monomers in the monomeric mixture are within certain limits which in general are different from those of the aforementioned mixtures of acrylonitrile, a-methylstyrene and styrene, and yet which are chosen in accordance with the same principle now to be discussed.

We have found that clear terpolymers of the nature described are made provided the proportions of three monomers in the monomeric mixture are chosen from the area lying along the line joining the binary polymerization azeotrope composition of acrylonitrile and the particular (b) on the one hand, and the binary polymerization azeotrope composition of acrylonitrile and the particular (c) on the other hand, as plotted on a triangular coordinate graph. By way of example, taking the case where (b) is a-methylstyrene and (c) is styrene, the point of the binary azeotrope composition of acrylonitrile and v -methylstyrene is placed along one side of' a triangular coordinate graph at the proper location between the apex designating 100 percent acrylonitrile and the apex designating 100- percent rx-methylstyrene. This point is 30 weight percent acrylonitrile and 70 weight per- CSX cent a-methylstyrene. On the opposite side of the equilateral triangle, consituting the triangular coordinate graph, is placed the point representing the binary azeotrope composition of acrylonitr-ile and styrene, this of course being located at the proper position on the side of the triangle between the apex representing 100 percent acrylonitrile and the apex representing 100 percent styrene. This point is approximately 24 weight percent acrylonitrile and 76 weight percent styrene. Now a straight line is drawn between these two points. This line cuts across the triangular coordinate graph without touching the side of the triangle opposite the acrylonitrile apex which side represents varying proportions of a-methylstyrene and styrene in binary mixtures of same. zt-Methylstyrene and styrene do not form a binary azeotrope. The said straight line joining the two points of binary azeotrope compositions describes three-component monomeric mixtures which, when subjected to free-radicalinitiated batch polymerization, give clear terpolymers. Further, there is an appreciable area lying on each side of said line in which the terpolymers are essentially clear. However, one cannot go too far from this line without producing terpolymers which are not clear but range from hazy to opaque materials. The invention particularly applies to the area lying within 5 percent on each side of said line; said 5 percent is measured on the graph in a direction normal to the line, and is equal to five-onehundredths of the shortest distance between an apex and the side of the triangle opposite that apex. (Another way of saying the same thing is that the invention particularly applies to the area of the graph bounded by two lines on opposite sides of and parallel to and 5 graphical units distant from said line.) Terpolymers made by polymerizing a monomeric mixture having a composition lying in the area within 5 percent on each side of the line joining the two binary polymerization azeotrope compositions, are generally clearer than polymers made from similar monomeric mixtures lying farther away from and on the `same side of the line. In most systems all terpolymers made from monomeric mixtures having compositions in the area lying within 5 percent on each side of the line are clear. In some systems the area of clarity may not extend as far as 5 percent from the line. Those skilled in the art, having had the beneit of the present disclosure, can easily determine by simple tests of the nature described herein which monomeric mixtures give clear terpolymers in a given polymerization system. ln all events, the compositions of monomeric mixtures giving clear terpolymers will be found to constitute an area lying along and encompassing the line joining the two binary polymerization azeotrope compositions.

The reasons for the clarity of terpolymers made as described are not known. The line joining the two binary azeotrope compositions does not represent what might be called a series of three-component azeotropes.

From much detailed data which we have obtained, the relative proportions of the three monomers in terpolymers made from monomeric mixtures lying along said line are not identical to the monomeric mixture from which the terpolymer is being prepared. In other words, during the course of a batch polymerization of a monomeric mixture whose composition is taken from the line, the composition `of residual monomeric material drifts and the terpolymers so formed are not homogeneous mixtures of polymer molecules all of which contain monomer units in the same ratio, but rather are mixtures of polymer molecules having varying proportions of the three monomer units therein. No heretofore known scientific facts or theories of interpolymerization explain our discovery. However, regardless of the various reasons for believing that terpolymers made from compositions lying along the line as aforesaid would be heterogeneous, and regardless of the actual reasons for the clarity of such terpolymers, it is apparent that the present invention makes possible the production of clear terpolymers with obvious attendant advantages, especially in films and molded articles made from the terpolymers.

The accompanying drawings are triangular coordinate graphs showing compositions of some threecomponent monomeric mixtures that give clear terpolymers on being subjected to free-radical-initiated batch polymerization.

Figure I represents the system -acrylonitrile/a-methylstyrene/styrene.

Figure II represents the system acrylonitrile/styrene/ vinyltoluene.

By the present invention we can subject a given monomeric mixture consisting of three monomers, selected as described herein, to a batch polymerization and carry the polymerization reaction to complete or essentially complete, say 90 to 100 percent, conversion of all of the monomers and yet obtain a clear solid resinous terpolymer. If desired, the polymerization can be stopped at any point short of completion so long as polymerization conditions are such as to produce solid terpolymer, but this is not necessary in order to obtain a clear terpolymer and would seldom be advantageous. The higher the degree of conversion of monomeric mixtures, the greater the advantages of our invention. This is -because the greatest extent of heterogeneity is found with complete conversion to polymers. A high conversion, i. e., at least 50 weight percent conversion and preferably 4at least 80 weight percent conversion, is preferred in practicing the invention. However, some of the benets of the invention may be realized even Where the percentage conversion is as low as 20 percent. With very low conversions, the polymer formed tends to approach the perfect homogeneity existing in the irst innitely small increment of polymer formed. As pointed out above, commercial practicality requires that conversion be carried to a value more than a few percent, hence introducing the lack of homogeneity which up to now, the art has not known how to avoid other than by techniques such as gradual monomer addition. It is to be recognized that the extent of the area of clear terpolymers, lying along the line joining the two binary polymerization azeotrope compositions, is dependent not only on the particular polymerization system but also on the percentage conversion, said area being the greater the lower the percentage conversion, and the smaller the higher the percentage conversion. It is observed that the terpolymers become clearer as the composition of the monomeric mixture approaches the line joining the two binary azeotrope compositions, the general rule being that the clearest terpolymers are those derived from monomeric compositions lying on the line.

It is usually desirable that the three-component monomeric mixture contain at least 2 weight percent, and preferably at least 5 weight percent, of the monomer present in the smallest amount.

The invention is broadly applicable to any free-radicalinitiated interpolymerization of three-component monomeric mixtures containing the monomer combinations and in the proportions set forth herein, provided the polymerization is carried out by a -batch procedure. By this it is meant that Iall of the monomeric materials to be employed are introduced simultaneously in the desired proportions into the polymerization reaction system. Ordinarily a single charge of monomeric materials will be placed in a reaction vessel and the single ,charge subjected to polymerization conditions until the polymerization is substantially complete. However, it is not outside the scope of our invention to introduce continuously a monomeric mixture containing the three monomers in lixed proportions into a ilow-type polymerization system, whereby the initial polymerizable mixture passes away from its point of introduction and ultimately is-recovered as polymer. This can be accomplished by continuous flowing of the monomeric mixture into the flrst of a series of polymerization reaction vessels with continuous llow of reaction mixture from one vessel to another along a series of two or more such vessels with ultimate recovery of polymer from the last in the series. Those skilled in the art will understand that this operation is essentially a batch operation in the sense that additional monomeric material of composition different from the original mixture is not introduced into a partially polymerized material. Thus, the term batch polymerization, as used herein, means a polymerization which does not involve the gradual or incremental or subsequent addition of a monomer or monomers having a composition dilferent from the initial monomeric mixture.

The invention is perhaps most advantageously eiected by the mass or -bulk polymerization procedure. In such procedure the reaction mixture is free from added solvent or other reaction medium and consists solely of monomers, resultant polymers, and catalyst and regulator, if any. An important advantage of the invention is that such a mass polymerization can be eected to produce a clear terpolymer in a situation in which it is impossible to use the gradual monomer addition technique discussed above.

lf desired, the interpolymers of the present invention can be made by the suspension or the emulsion polymerization techniques. For suspension polymerization a reaction medium such as water .is used together with a small yamount of suspending agent, for example, tricalcium phosphate, carboxymethylcellulose, etc., to give a suspension of particles of initial monomeric mixture, which particles are not of such small size as to result in a permanently stable latex. Where the particles are of quite large size, this type of polymerization is often called pearl polymerization. To effect emulsion polymerization, sufficient amount of emulsifyiug agent, for example a water-soluble salt of a sulfonated long chain alkyl aromatic compound, a surface active condensation product of ethylene oxide with long chain aliphatic alcohols or mercaptans, etc., is employed along with vigorous agitation whereby an emulsion of the reactants in water is formed and the product is obtained in the form of a latex. The latex can then be coagulated if desired by known methods and the polymer separated from the water. For some applicationsthe latex can be employed directly as for example for forming a lm, and the resulting lm after evaporation of the water will be clear when the polymers are made in accordance with the presont invention. The emulsion technique has certain advantages-particularly in that a very high degree conversion of the monomers is obtained with considerable rapidity, since the heat of reaction is easily carried `oil by indirect heat exchange with the reaction mixture which contains a considerable proportion of water. Such polymerizations are often effected with redox-type catalyst systems at moderate temperatures of say 60 C. on down to 0 C. and below.

The polymers of the present invention can also be made in the presence of an added organic solvent. It shouldbe recognized however that the presence of such a solvent ordinarily results in a polymer of lower molecular weight than that obtained in the absence ofthe solvent.

Conventional recipes and procedures for effecting mass, solvent, suspension and emulsion polymerizations are so well-known to those skilled in the art, that they need not be further detailed here.

From the foregoing, it will be apparent that the term, monomeric mixture, as used in the claims refers only to the polymerizable monomeric materials used in the process, and that additionally solvents, aqueous reaction media, catalysts, etc., can be present or not in the reaction mixture as may be desired in any particular case. In other words, in the claims monomeric mix- ,tureis not necessarily synonymous with reaction mixture.

Polymerization can be effected by any of the wellknown free radical mechanisms. The polymerization is initiated and carried on by virtue of free radicals, which can be derived from the monomers themselves on simple heating of the monomeric mixture to a suitable temperature, or can be derived from added free-radicalsupplying catmysts, especially the per compounds and the azo compounds, or can be derived by ultraviolet or other irradiation of the reaction mixture with or without the presence of photosensitizers, e. g., organic disulfides. The examples set forth hereinafter describe thermal polymerizations in whichl the polymerization reaction was initiated and maintained merely by heating the monomeric mixture in the absence of any added catalyst. ln many instances it will be desired to add a suitable polymerization catalyst, in which case sufficient catalyst is employed to give a desired reaction rate. Suitable catalysts are of the free-radical-promoting type, principal among which are peroxide-type polymerization catalysts, and azo-type polymerization catalysts. Those skilled in the art are now fully familiar with a large number of peroxide-type polymerization catalysts and a suitable one can readily be chosen by simple trial. Such catalysts can be inorganic or organic, the latter having the general formula: ROOR, wherein R is an organic radical and R is an organic radical or hydrogen. These compounds are broadly termed peroxides, and in a more specific sense are hydroperoxides when R is hydrogen. R and R can be hydrocarbon radicals or organic radicals substituted with a great variety of substituents, By way of example, suitable peroxide-type catalysts include benzoyl peroxide, ditertiary butyl peroxide, tertiary butyl hydroperoxide, diacetyl peroxide, diethyl peroxycarbonate, Z-phenyl propane-2-hydroperoxide (known also as cumene hydroperoxide) among the organic peroxides; hydrogen peroxide, potassium persulfate, perborates and other per compounds among the inorganic peroxides. The azotype polymerization catalysts are also well-known to those skilled in the art. These are characterized by the presence in the molecule of the group NIN- bonded to one or two organic radicals, preferably at least one of the bonds being to a tertiary carbon atom. By way of example of suitable azo-type catalysts can be mentioned a,a'-azodiisobutyronitrile, p-bromobenzenediazonium lluoborate, N-nitroso-p-bromoacetanilide, azof methane, phenyldiazonium halides, diazoaminobenzene, p-bromobenzenediazonium hydroxide, p-tolyldiazoaminobenzene. The peroxy-type or azo-type polymerization catalyst is used in small but catalytic amounts, which are generally not in excess of one percent by weight based upon the monomeric material. A suitable quantity is often in the range of 0.05 to 0.5 percent by Weight.

Photopolymerization is another suitable procedure for carrying out the present invention. This is ordinarily accomplished by irradiating the reaction mixture with ultraviolet light. Any suitable source of light is employed having effective amounts of light with wave lengths of 2,000 to 4,000 Angstrom units. The vessel in which the polymerization is conducted should be transparent to light of the desired wave length so that the light can pass through the sides of the container. Suitable glasses are available commercially and include borosilicate (Pyrex), Vycor, and soft glass. Alternatively, the source of light can be placed directly over the surface of the monomer in a container or can be placed within the reaction mixture itself. In some instances it is helpful to add a material that can be termed a photosensitizer, i. e., a material which increases the rate of photopolymerization, for example organic disulfides as described in U. S. Patent No. 2,460,105.

Choice of a suitable temperature for a given polymerization will readily be made by those skilled :in the art having been given the benet of the present disclosure. In general, suitable temperatures will be found within the range of 0 C. to 200 C., although temperatures outside this range are not beyond the scope of the invention in its broadest aspects. The time required for complete polymerization will depend not only upon the temperature but also upon the catalyst if any is employed, the ability of the system to remove heat of polymerization, and the particular monomers employed. The examples set forth hereinafter give some illustrative information as to reaction times for particular polymerizations.

The term .triangular coordinate graph as used herein is well understood. The accompanying figures are examples of such graphs and the use of same. However, for the sake of completeness the following statement can be made concerning the character of such triangular graphs. rl'he graph is an equilateral triangle, divided off by three series of parallel lines each series being parallel to one side of the triangle. The distance between an apex of the triangle and the side opposite that apex represents variations in percentages of the component designated by that apex varying from percent to 0 percent in equal increments running from the apex to the opposite side of the triangle. For example, if the distance between the apex and the side of the triangle opposite the apex is divided into 100 equal parts by lines passing across the triangle and parallel to said side, each line represents l percent of the component for which that apex is designated. Thus, any point within the triangle represents a single three-component composition, the indicated percentages of the three components totaling l0@ percent.

As an aid in the choice of suitable proportions of monomers for polymerization in accordance with the invention the following data on reactivity ratios of certain monomer pairs are presented by way of example. The values given are considered the best ones represented in the literature or otherwise known, (see Copolymers by Alfrey, Bohrer and Mark, Interscience Publishers, inc., 1952, pp. 32-43). In many instances an attempt is made to set forth an approximate order of accuracy. These latter figures, expressed as plus or minus certain values, should not however be given too much credence since such attempts to evaluate possible errors are dependent to a considerable extent on subjective evaluation of the data. Most of the values for reactivity ratios given are for moderate temperatures, say between about room temperature (20 C.) and 100 C. Of course, the value of thc reactivity ratios for a monomer pair is a function of temperature but the variation in reactivity ratios with temperature is quite small and is of little importance unless the polymerization is to be carried out at temperatures considerably removed from those mentioned. Liliewise, the reactivity ratios given are for atmospheric or autogenous pressure. Only if the polymerization pressure is to be quite considerably increased will there be an important change in the value of the reactivity ratios. lt may also be pointed out that inthe case of highly wa ,rsoluble monomers the reactivity ratio values may be shifted somewhat from those given, w en polymerization is effected in an aqueous system. Those skilled in the art, having been given the benefit of the present disclosure, will be able to evaluate the effect, if any, of reaction conditions on the values given herein and determine the extent of such effect. Similarly, those skilled in the art can determine by well-known procedures the correct reactivity ratios for monomer pairs not specifically set forth in the following tabulation, which tabulation is given by way of example of some but not all of the monomers that are the subject matter of the present invention.

In the following tabulation each monomer in a pair is designated as M1 or M2. Substitution of the values for r1 and r2 in the equation given above for the binary polymerization azeotrope composition permits an immediate determination of the proper location for the two points to be placed on the triangular coordinate graph, between which points is drawn the line of clear terpolymers.

Where M1 is to be vinyltoluene or vinylxylene, the reactivity ratios given above for acrylonitrile/styrene are used, on the assumption that the reactivity ratios for the systems acrylonitrile/vinyltoluene and acryionitrile/ vinylxylene do not differ essentially for the purposes lof this invention from the reactivity ratios of the corresponding system wherein styrene is M1. This assumes that the introduction of one or two methyltgroups into the aromatic nucleus of styrene does not greatly -alter the polarity and steric properties of the vinyl double bond. Whenever weight percent rather than mole percent is desired as a matter of convenience, mole percentages of the binary azeotrope compositions are easily converted to weight percent by use of the molecular weights of the particular M1 and M2.

The following examples illustrate some methods for practicing the present invention with respect to certain ternary mixtures of monomers. The general applicability of the invention, and advantages thereof, are shown in these examples. It will be appreciated that variations can be made in the particular choice of monomers, proportions, and methods of polymerization in accordance with the general teachings of the present specification, and that the examples are not to be taken as coextensive with the invention in its broadest aspects.

Example .I

This example concerns the ternary system acrylonitrile/ styrene/a-methylstyrene. The data obtained in this exampleare set forth graphically in Figure l of the drawing.

The composition of the acrylonitrile/afrnethylstyrene binary azeotrope was calculated in the following manner according to the article by Mayo and Walling, Chemical Reviews 46, 199 (1950).

Acrylonitrile (M 1) a-Methylstyrene M2) T1: o. 0 6

[M2l-l-0.96 [M2l1=100=1;96 [M2] [M2lr=51 mole percent -methylstyrene [rl/111:49 mole percent acrylonitrile Molecular lweight of amethylstyrene=l 18.17 Molecular weight of acrylonitrile 53.06 0.51 l18.17r=60.3 grams a-methylstyrene 0.49 53.06=26.0 grams acrylonitrile 86.3 grams mixture (60.3 100) /86.3=70 weight percent a-Inethylstyrenc (26.0X100)/86.3r=30 weight percent acrylonitrile The foregoing calculations give the composition of the acrylonitrile/a-methylstyrene binary polymerization azeotrope as weight percent acrylonitrile, 70 weight percent rat-methylstyrene.

By the same procedure, the binary polymerization azeotrope for acrylonitrile/styrene was calculated to be 24 weight percent acrylonitrile, 76 weight percent styrene.

A series of monomeric mixtures was made up, each mixture being prepared by admixture of the individual pure monomers in a Pyrex test tube 150 mm. long and having an internal diameter withinthe approximate range of 14 to 18 mm., usually about 16 mm. VEach test tube containing the particular monomeric mixture wasiushed with nitrogen in order to remove any air present in the gas space above the liquid, and the test tube was then sealed oft at the top by heating the tube under nitrogen and pulling it out in the ame to seal the tube completely. Each particular monomer mixture was prepared and polymerized in duplicate.

After the various tubes containing the monomeric mixtures -had been prepared, they were placed in a 90 C. constant temperature bath, and held there for 24 hours.

' At the end of that period they were moved to a 120 C.

f given.

constant temperature bath and held there for 24 hours. At the end of this second 24-hour period the tubes were removed and placed in an oven maintained at C. and held therein for 8 hours.

The various monomeric compositions are set forth in detail in Table I which follows. Table I designates each different mixture by sample number. Samples Nos. 3, i3, 38, 39, 29, 33 and 40 constitutea series of samples having compositions falling on or nearest to the straight line connecting the two binary azeotrope compositions whose percentage values were calculated as given above, when plotted on triangular coordinates. See Figure All of the samples were prepared with compositions which vary so that several Yseries of from three to seven different compositions running along constant fx-methylstyrene composition lines and cutting across the line joining the two binary azeotropes could be examined.

t the end of the polymerization cycle described above, all the polymers formed in the sealed tubes were carefully examined visually by the same observer, looking through the diameter f the cylindrical body of polymer `obtained by breaking and removing the glass tube; this cylinder of polymer conformed to the internal shape and size of the glass tube. These -visual observations were checked by other observers. It was determined that the clarity noted for polymer samples is not significantly affected by variation in polymer cylinder diameter within the range of about 14 to 18 millimeters. It -is to be understood that where clarity of polymers is discussed herein, reference is made to the appearance on looking through a cylindrical body ot the polymer having a diameter within the approximate range of 14 to 18 millimeters. The following words were adopted for describ ing the clarity ofpolymers:

C-Clear-essentially crystal clear H--Hazy-some cloudiness but slight T-Turbid-moderately cloudy O-Opaquedense cloudiness-similar to milk glass in appearance Clear means relatively free from gross amounts of haze but allows the presence of slight haze to be detected with close examination in strong light. Specic'notation that a sample was crystal. clear means not only that no haze was apparent tothe observer, but also that the sample showed a sparkling appearance as found in high quality crystal glassware.

The alcohol solubles content of some of the polymers was deter-mined, using the followingrstandard procedure:

An 0.3 gram-sample of polymer' is dissolved in 20 ml. acetone (or other suitable solvent), then the polymer is precipitated by adding 250 ml. absolute ethanol to the solution; the precipitate is coagulated, filtered olf, dried and weighed. The average of two determinations is The alcohol solubles content (ASC) gives an approximate measure of the extent of conversion. rlhe material solublein alcohol is principally monomer; only very low molecular weight polymers, e. g., dimers and trimers, are soluble in alcohol. Thus 10U-ASC approximates the percentage conversion.

The specific viscosity was determined on the total polymer, and on thefundissolved residue from the alcohol solubles test, inra number of instances. The specific viscosity'.determinationsiwere made on a 0.1 weight percent solution Of polymer in dimethylforamide,

TABLE I.-ACRYLONITRlLE/STYRENE/a-METHYLSTYRENE TERPOLYMERS Appearance Composi- Sample No. tion, Wt.. Percent a- MS [AN/S Clarity Color Alcohol Solubles Content, Wt. Per- Total Alcohol cent Polymer Insoluble Residue Specific Viscosity a-MS a-Methylstyrene. AN Acrylonltrile. S Styrene.

Referring now to Figure I of the drawings, the clarity data given in Table I have been designated alongside of each of the corresponding ternary monomeric mixture compositions indicated by the point on a triangular coordinate plot. The various numerals on Figure I located adjacent the respective points refer to the sample number in Table I. All of the points marked C were rated as clear, and of these all were crystal clear with the exception of the sample represented by point 35 which had a very slight haze but not suiicient to consider it other than essentially clear or to bring it from the clear rating into the hazy rating. Examination of Figure I immediately shows that terpolymers prepared from monomeric mixtures having compositions lying on the line joining the two binary azeotrope compositions were clear, as were terpolymers within the area lying along said line. However, going appreciably beyond 5 percent on each side of the line the terpolymers become non-clear. Opacity increases more quickly below the line as higher concentrations of styrene and lower concentrations of methylstyrene are approached and to a lesser extent as lower concentrations of acrylonitrile are approached, than it does on the opposite side of the line and at the lower end of the line approaching zero percent styrene. Thus, in the present system acrylonitrile/ styrene/ a-methylstyrene, point 4, which is 4 percent away from the line on the lower side of the line, and point 9 which is 5 percent away from the line on the same side, are opaque, so that the area of perfectly clear terpolymers along the line does not extend quite to the 5 percent line in this portion of the graph. It can be stated generally that on the lower side of the line (the side opposite the 100 percent acrylonitrile apex) all polymers within 3 percent of the line are clear and many polymers farther away than 7 5 percent are also clear, especially in the direction of ecreasing styrene content. All polymers on the opposite side of the line and Within 5 percent of the line are clear as are some more than 5 percent away from the line. With respect to points 4 and 9 it will `be noted even here that these points are much clearer, being only turbid, than are the adjacent points 5 and l0 respectively which are farther away from the line and are opaque. The appearance of opacity and turbidity closer to the line in some regions than in other regions are consistent with most physical phenomena which seldom exhibit perfect regularity. The data in the present example demonstrate that terpolymers made from ternary monomeric mixtures whose composition is taken from along the line and from a significant area lying on each side of the line are clear, and thus constitute a new group of terpolymers having the extremely important property of clarity. Another interesting thing to note is that by the practice of the present invention terpolymers of minimum color ordinarily result. This is easily seen by observing in Table I the recorded color of each of the samples and comparing it with the location on Figure I. The samples containing the larger proportions of acrylonitrile appear to have the greatest amount of yellow color. Clear samples lying within the area of clear terpolymers along the line have no color provided they contain less than 40 weight percent a-methylstyrene, while those containing more than 40 weight percent a-methylstyrene have a slight yellow color. Of these latter samples, the samples on and nearest the line are less colored than those farther away from the line.

In Figure I the dashed lines drawn parallel to-the line joining the two binary azeotrope compositions are 5 percent on each side of the line, i. e., each is a distance from 13 the line equal to percentage points of composition as .determined by dividing the distance between'an apex and thefcenter of the opposite side of the triangle vinto 100 equal equidistant parts; in other words, the two dashed lines are on opposite sides of and 5 graphical units distant fromsaid line.

Example 2 This example presents data on the ternary system acrylonitrile/styrene/vinyltoluene.

In the manner set forth in Example 1, the binary polymerization azeotrope composition of acrylonitrile/-styrene was calculated to be 24 weight percent acrylonitrile and 76 weight percent styrene.

The reactivity ratios for the system acrylonitrile/vinyltoluene were assumed not to differ essentially for the purposes of this invention from the reactivity ratios of the corresponding system acrylonitrile/styrene. This assumes that the introduction of a methyl group into the aromatic nucleus of styrene does not greatly alter the polarity and stearic properties of the vinyl double bond. Accordingly, as M1, and the reactivity ratios as r1=0.41 and r2=0.03. Moleratios for the binary polymerization azeotrope were calculated in the manner described in the preceding example, and these were then converted to weight ratios, employing the molecular weights of acrylonitrile and vinyltoluene. The thus-calculated value of the binary azeotrope composition is 22 weight percent acrylonitrile, 78 weight percent vinyltoluene.

The vinyltoluene used in these tests was a mixture of isomeric metaand para-methylstyrenes,

Samples containing varying proportions of the monomers were prepared and polymerized and observations made on the polymers in the manner described in Example 1. The data are listed in Table II and plotted in Figure Il of the drawings.

TABLE Il.-STYRENE/ACRYLONITRILE/VINYL- S Styrene. AN Acrylonitrile. VT vinyltoluene.

'Ihe data of Table II, particularly as plotted on Figure l1, again show the clarity `of terpolymers prepared from monomeric mixtures, whose composition is taken from the line joining the two binary polymerization azeotrope compositions. As in Example 1, with the acrylonitrile/styrene/a-methylstyrene terpolymers, opacity increases -more quickly on the side of the line representing decreasing amounts of acrylonitrile than it does on the side representing increasing amounts of acrylonitrile. Thus, in the present system acrylonitrile/styrene/vinyltoluene, points 6 and 7, which are about l2 percent away from the line on the side of increasing acrylonitrile content, are only hazy whereas points 8 and 9 on the opposite side of the line an approximately equal distance were both opaque. ln this system the clear area lying along the line includes that within 5 percent on each side of the line and extends appreciably beyond the 5 percent line.

While the invention has been described with particular reference to various preferred embodiments thereo'f, and examples have been given of suitable proportions acrylonitrile was taken as M2, vinyltoluene and conditions, it will be appreciated .that variations from 'the details fgiven herein can vbe effected without departing lfrom the'invention. When desired, the terpolymers of the present invention can be blended with other polymers, plasticizers, solvents, fillers, pigments, dyes, stabilizers, and'the like, in accordance with the particular use intended.

We claim:

`1. A clear `terpolymer prepared by free-radical-initiated batchV polymerization 'of 'a monomeric mixture consisting of (a) acrylonitrile, (b) a monomer selected 'from the group consisting of a-acetoxystyrene, u-m-ethylstyrene, styrene, vinyltoluene, vinylxylene, and (c) a different monomer selected from said group, the proportionsof the three monomers in said monomeric mixture being limited to those in the area 'of mixtures that produceclear terpolymers, said 'area `.encompassing the line joining th-e polymerization azeotrope composition of .acrylonitrile and lthe particular (b) on the one .hand

and acrylonitrile and the particular (c) on the other hand as plotted on an equilateraltriangular coordinate graph.

2. A terpolymer according to claim l wherein one of said monomers is styrene.

3. A terpolymer according to claim `1 wherein one of said monomers is a-methylstyrene.

4. A terpolymer according to claim 1 wherein one of said monomers is vinyltoluene.

.5. A terpolymer according yto claim 1 wherein said three monomers are acrylonitrile, styrene and a-methylstyrene.

6. A terpolymer according to claim l wherein said three .monomers are acrylonitrile, styrene, and vinyltoluene.

7. A clear terpolymer prepared by free-radical-initiaated batch mass'polymerization 'of a monomeric mixture consisting of (d) acrylonitrile, (b) a monomer selected from the group'consisting of a-acetoxystyrene, a-methylstyrene, styrene, vinyltoluene, vinylxylene, and (c) a different monomerselecte'd from said group, the proportions 'of the three monomers in said monomeric mixture being limited to those in the area of mixtures that produce cleai vterpolymers, said area encompassing the line joining the polymerization azeotrope composition of acrylonitrile and the particular (b) on the one hand and kacrylonitrile and the particular (c) on the other hand as plotted on an equilateral triangular coordinate graph.

8. A terpolymer according to claim 7 wherein one of the said monomers is styrene.

9. A terpolymer according to claim 7 wherein one of of said monomers is a-methylstyrene.

10. A terpolymer according to claim 7 wherein one of said monomers is vinyltoluene.

1l. A terpolymer according to claim 7 wherein said three monomers are acrylonitrile, styrene, and 1c-methylstyrene.

12. A terpolymer according to claim 7 wherein said three monomers are acrylonitrile, styrene, and vinyltoluene.

13. A clear terpolymer prepared by free-radical-initiaated batch polymerization to a conversion of at least 20 weight percent of a monomeric mixture consisting of (a) acrylonitrile, (b) a monomer selected from the group consisting of a-acetoxystyrene, -methylstyrene, styrene, vinyltoluene, vinylxylene, and (c) a different monomer selected from said group, the proportions of the three monomers in said monomeric mixture being limited to those in the area of mixtures that produce clear terpolymers, said area encompassing the line joining the polymerization azeotrope composition of acrylonitrile and th-e particular (b) on the one hand and acrylonitrile and the particular (c) on the other hand as plotted on an equilateral triangular coordinate graph.

14. A polymerization process which comprises forming a three-component monomeric mixture consisting of (a) acrylonitrile, (b) a monomer selected from the group consisting of a-acetoxystyrene, a-methylstyrene, styrene, vinyltoluene, vinylxylene, and (c) a different monomer selected from said group, the proportions of the three monomers in said monomeric mixture being limited to those in the area of mixtures that produce clear terpolymers, said area encompassing the line joining the polymcrization azeotrope composition of acrylonitrile and the particular (b) on the one hand and acrylonitrile and the particular (c) on the other hand as plotted on an equilateral triangular coordinate graph, and subjecting a batch of said monomeric mixture to free-radicalinitiated batch polymerization forming an essentially clear homogeneous high molecular weight terpolymer.

15. A polymerization process according to claim 14 wherein said polymerization is effected in mass.

16. A polymerization process according to claim 14 wherein one of said monomers is styrene.

17. A polymerization process according to claim 14 wherein said three monomers are acrylonitrile, styrene, and a-methylstyrene.

18. A polymerization process according to claim 14 wherein said three monomers are acrylonitrile, styrene, and vinyltoluene.

19. A clear terpolymer prepared by free-radicalinitated batch polymerization of a monomeric mixture consisting of (a) yacrylonitrile (b) a monomer selected from the group consisting of -acetoxystyrene, a-methylstyrene, styrene, Vinyltoluene, vinylxylene, and (c) a different monomer selected rom said group, the proportions of the three monomers in said monomeric mixturebeing limited to those in the area of mixtures that produce clear terpolymers, said area encompassing the line joining the polymerization azeotrope composition of acrylonitrile and the particular (b) on the one hand and acrylonitrile and the particular (c) on the other hand as plotted on an equilateral triangular coordinate graph, with the further limitation that said proportions of the three monomers are restricted to the area of said graph bounded by two lines on opposite sides of and parallel to and 5 graphical units distant from said line.

20. A clear terpolymer prepared by free-radicalinitiated batch polymerization of a monomeric mixture consisting of (a) acrylonitrile (b) a monomer selected from the group consisting of a-acetoxystyrene, tnt-methylstyrene, styrene, vinyltoluene, vinylxylene, and (c) a different monomer selected from said group, the proportions of the three monomers in said monomeric mixture being designated by the line joining the polymerization azeotrope composition of acrylonitrile and the particular (b) on the one hand and acrylonitrile and the particular (c) on the other hand as plotted on an equilateral triangular coordinate graph.

21. A terpolymer according to claim 20 wherein said three monomers are acrylonitrile, styrene, and a-methylstyrene.

22. A clear terpolymer prepared by free-radicalinitiated batch polymerization of a monomeric mixture consisting of (a) acrylonitrile (b) styrene, and (c) amethylstyrene, the proportions of the three monomers in said monomeric mixture being limited to those in the area of mixtures that produce clear terpolymers, said area encompassing the line joining the polymerization azeotrope composition of acrylonitrile and styrene on the one hand and acrylonitrile and a-methylstyrene on the other hand as plotted on an equilateral triangular coordinate graph, with the further limitation that said proportions of the three monomers are restricted to the area of said graph 4bounded by two lines on opposite sides of and parallel to and 5 graphical units distant from said line.

23. A terpolymer according to claim 22 wherein the proportion of a-methylstyrene is less than 40 weight percent.

24. A clear terpolymer prepared by free-radicalinitiated batch polymerization of a monomeric mixture consisting of (a) acrylonitrile (b) styrene, and (c) vinyltoluene, the proportions of the three monomers in said monomeric mixture being limited to those in the area of mixtures that produce clear terpolymers, said area encompassing the line joining the polymerization azeotrope composition of acrylonitrile and styrene on the one hand and acrylonitrile and vinyltoluene on the other hand as plotted on an equilateral triangular coordinate graph, with the further limitation that said proportions of the three monomers are restricted to the area of said graph bounded by two lines on opposite sides of and parallel to and 5 graphical units distant from said line.

References Cited in the iile of this patent FOREIGN PATENTS 

1. A CLEAR TERPOLYMER PREPARED BY FREE-RADICAL-INITIATED BATCH POLYMERIZATION OF A MONOMERIC MIXTURE CONSISTING OF (A) ACRYLONTRILE, (B) A MONOMER SELECTED FROM THE GROUP CONSISTING OF A-ACETOXYSDTYRENE, A-METHYLSTYRENE, STYRENE, VINYLTOLUENE, VINYLXYLENE, AND (C) A DIFFERENT MONOMER SELECTED FROM SAID GROUP, THE PROPORTIONS OF THE THREE MONOMERS IN SAID MONOMERIC MIXTURE BEING LIMITED TO THOSE IN THE AREA OF MIXTURES THAT PRODUCE CLEAR TERPOLYMERS, SAID AREA ENCOMPASSING THE LINE JOINING THE POLYMERIZATION AZEOTROPE COMPOSITION OF ACRYLONITRILE AND THE PARTICULAR (B) ON THE ONE HAND AND ACRYLONTRILE AND THE PARTICULAR (C) ON THE OTHER HAND AS PLOTTED ON AN EQUILATERAL TRINGULAR COORDINATE GRAPH. 